Conventional elevator safety equipment includes an overspeed governor for impeding elevator car movement when a predetermined speed is exceeded. Overspeed governors include a switch that opens when the elevator reaches a predetermined overspeed such as 110% of rated speed. When the switch opens, power is removed from the machine motor and brake. A braking mechanism, actuated in response to movement of the elevator car by motion transmission means, impedes the elevator car. The switch remains open, and the elevator remains inoperable, until the switch is manually re-set.
Typical governor designs include a sheave coupled to a rope attached to the elevator car, whereby the sheave moves in response to rope movement indicative of elevator car movement. The sheave drives a shaft or spindle coupled to an actuation mechanism. The actuation mechanism may be a set of flyballs or flyweights adapted to extend radially when a predetermined level of centrifugal force is applied to them. Radial extension of the flyballs or flyweights causes them to contact an overspeed switch When the overspeed switch is actuated, power to the motor and motor brake is cut, thereby causing the motor brake to apply a braking force on the motor shaft. If the elevator car continues to increase in speed, a tripping assembly is triggered by the fly weights. The tripping assembly actuates a mechanism to brake the governor rope. Braking of the governor rope causes the Safeties to be engaged and thereby stop the car.
Because the overspeed switch remains open until it is manually re-set, the elevator machine and brake power are not restored and the elevator system remains inoperable. In conventional elevator systems having machine rooms the switch to be re-set is conveniently accessible in the machine room by a technician. Typically, the governor is located in an overhead machine room.
In more recently developed "machine room-less" elevator systems, where the conventional machine room is eliminated, the governor and various other components are located in the hoistway. With the governor in the hoistway, the task of accessing and re-setting a governor overspeed switch is time-consuming, complicated, and costly. Although a solution may be to provide a special door or hatch to access a governor in a hoistway, such a solution adds cost and space requirements.
It is an object of the present invention to provide an overspeed switching system that operates safely and reliably, while reducing time and cost of restoring an elevator to operation after the overspeed switch has been tripped. These objects and others are achieved by the present invention.
The present invention is directed to an overspeed switch system for an elevator where a first switch located in the governor is tripped in response to detected overspeed, and the tripping of the first switch causes a second, remotely located switch to be tripped, whereby when either or both switches are open, power to the elevator system is shut down. The first switch is provided with automatic re-set means, while the second switch is manually re-set in an easily accessible, remote location such as a control panel in a landing.